The latest build of Windows Mobile uploaded by Da_G bears a new name. The builds of WM6.5.5 have (as far as Iâ€™ve noticed) started from 235XX, and the latest is 23518. WM6.5.3 was the WMD branch, and is builds 28001 and above.
This latest release brings a few changes, notably the inclusion of Office Mobile 2010 (more detail on that here) and threaded email.
As far as I can tell, the â€œWM6.5.5â€ part is pretty much meaningless, but itâ€™s nice to see the improvements in WM getting gradually developed.
Itâ€™s available for a variety of devices on XDA-Developers, including a Diamond ROM by me available here.